One type of fuel that is used to power internal combustion engines and other fuel consuming devices is a gaseous fuel such as natural gas in the form of compressed natural gas (CNG) or liquefied propane gas (LPG). Fuel injectors for supplying a metered amount of gaseous fuel to a fuel consuming device such as an internal combustion engine are well known. In a typical fuel injector, a valve is located in a fuel passage of the fuel injector and is axially reciprocated in and out of contact with a valve seat to control the flow of fuel through the fuel injector. A common failure in gaseous fuel injectors at cold temperatures is for the valve to stick closed. Gaseous fuels do not have the lubricity that liquid fuels possess. This lack of lubricity allows moisture to condense and freeze on the fuel injector internal components when the internal combustion engine is not running and the fuel injector is allowed to cool to ambient temperature, thereby causing the internal components of the fuel injector to be bound together and preventing the valve from being opened.
Another shortcoming of some prior art gaseous fuel injectors is that the valve seat can be distorted when it is welded to the fuel injector or valve seat carrier during the manufacturing process due to the heat generated during the laser welding process and the close proximity of the weld to the seating surface of the valve seat. Misalignment due to lost parallelism of the valve seat with the valve may occur which can result in unsatisfactory performance of the fuel injector if the seating surface of the valve seat becomes distorted.
In order to prevent gaseous fuel injectors from sticking closed at cold temperatures it is known to provide a shroud or cap over the fuel outlet of the fuel injector. An example of a prior art fuel injector with a shroud is shown in FIG. 1. Fuel injector 10 includes fuel inlet 14 for receiving fuel, fuel outlet 16 for dispensing fuel, and fuel passage 18 for communicating fuel from fuel inlet 14 to fuel outlet 16. Valve assembly 20 is provided for selectively preventing and permitting fuel to pass from fuel inlet 14 to fuel outlet 16. Valve assembly 20 includes valve seat 22 located in fuel passage 18. Valve seat 22 includes apertures 40 for providing fluid communication therethrough. Valve assembly 20 also includes valve 42 with valve tip 41 located in fuel passage 18 for selectively preventing and permitting fuel to pass through apertures 40. In order to prevent valve 42 and valve tip 41 from being stuck shut at cold temperatures due to moisture condensing and freezing on the fuel injector internal components, shroud 43 is placed over fuel outlet 16. Shroud 43 may be made by machining or stamping and may be fixed to fuel injector 10 by welding, crimping, press fit, or any other known method. Shroud 43 may be cup shaped and include one or more fuel exit passages 44 to allow fuel to exit therefrom. Shroud 43 impedes gas flow and thereby prevents moisture from condensing on the valve components that would cause valve 42 and valve tip 41 to be stuck shut in cold conditions. However, shroud 43 requires addition components and processing to fuel injector 10 and therefore adds cost.
A second example of a prior art fuel injector is shown in FIG. 2. Fuel injector 10′ shown in FIG. 2 is essentially the same as fuel injector 10 as shown in FIG. 1 with the exception of valve assembly 20′ which includes valve seat 22′. In the prior art example shown in FIG. 2, valve seat 22′ includes a separate and distinct disk 34 with apertures 40′. Disk 34 is welded within body 24 to complete valve seat 22′. As mentioned previously, welding disk 34 within tubular body 24 can cause valve seat 34 to become distorted which can result in unsatisfactory performance.
What is needed is a gaseous fuel injector that is less susceptible to sticking closed in cold conditions while requiring fewer components and less processing to the fuel injector compared to prior art fuel injectors with shrouds. What is also needed is a gaseous fuel injector that is less susceptible to valve seat distortion when the valve seat is secured to the fuel injector in the manufacturing process.